The "Send letter" action sends a PrintMailing to the profile entering the node.
Please note that there are costs involved in sending a Print mailing.
Under "Letter" you select the PrintMailing that is to be sent to the profile.
If the "Mailing protection" option is activated, only profiles that are not on the blacklist are loaded. If the option is deactivated, profiles are sent regardless of the blacklist. Permission and advertising consent is not checked for letters.